1. Field of the Invention
This invention relates to a method of forming oxide from nitride, more particularly to a process for wet oxidizing nitride enhanced by illumination with UV light.
2. Description of Prior Art
IC components are normally made of silicon. However, components made of silicon usually malfunction when operated at a high-temperature. In order to address this issue, it is desirable to fabricate IC components using III-V semiconductor materials since such components operate normally in a large temperature range. Furthermore, III-V semiconductor materials can be used to fabricate light-emitting devices. Recently, research into light-emitting devices has been focused on devices emitting light having a shorter wavelength, such as yellow, green or blue light. One of the most important materials used in the fabrication of such light-emitting devices is GaN.
The oxidation of single crystal gallium nitride has been investigated because of its importance in many electronic and optoelectronic applications, especially in achieving desired performances of III-V or II-VI semiconductor optoelectronic devices. For example, gallium oxide can serve as a growth template of a laser diode and form surface passivation, isolation, and AR coatings in semiconductor devices. The use of gallium oxide in the above applications can lead to a significant improvement.
Referring to FIG. 1, which indicates the increase of photo-response on the oxidized GaN due to the combination effects of surface passivation and index matching, in which curve A represents the photo-current response of Ga.sub.2 O.sub.3 and curve B represents the photo-current response of GaN. Furthermore, referring to FIG. 2, the data reveals the enhancement of PL intensity on the oxidized GaN region due to the index matching and surface passivation, wherein curve A' indicates Ga.sub.2 O.sub.3 /GaN and curve B' indicates GaN.
It is well known to those skilled in the art that a major shortcoming of GaAs-based semiconductor materials is the relatively poor quality and/or instability of the semiconductor/insulator interfaces typically produced by prior art methods. In the prior art, a conventional thermal oxidation technique is normally used to form oxide on GaN material. For example, "X-ray photoelectron spectroscopy and x-ray diffraction study of the thermal oxide on GaN", Appl. Phys. Lett. 70, p. 2156-2158 (1997), by S. D. Wolter, et al, discloses the production of Ga.sub.2 O.sub.3 when GaN is reacted with hot dry air. In this prior art, the oxidation starts gradually at 900.degree. C. and the growth rate of Ga.sub.2 O.sub.3 is only about 20 nm/hr. However, "High temperature surface degration of III-V nitrides," J. Vac. Sci. Technol. B 14, p. 3523-3531 (1996), C. B. Vartuli et al. indicates that the thermal process results in the evaporation of the nitrogen atoms of the mixed material InAlN/InGaN serving as the active region of the light-emitting device. For the mixed material InAlN/InGaN, gallium coagulates in the form of droplets when nitrogen evaporates at around 800.degree. C. and 900.degree. C., causing the degradation of the optical characteristics and surface flatness of the device.
"The anodic oxidation of GaAs in aqueous H.sub.2 O.sub.2 solution," J. Electrochem. Soc. 120, p. 1358-1390 (1973), A. Logan et al., discloses another growing technique of gallium oxide in which an anode electrolysis process is used by applying a bias voltage to GaAs dipped in electrolyte, thus forming gallium oxide by the effect of bias current. However, the thickness of the oxide formed by this method is limited. An applied voltage of about 100.about.200 volts is required to achieve an oxide thickness of about 2000 .ANG. since the bias voltage has to be increased proportionate to the thickness of the oxide. In other words, the electric field required to be applied to the interface of oxide and semiconductor is nearly 106.about.107 volts/cm, which is over the breakdown voltage of about 105 volts/cm for normal semiconductor material. Hence, the quality of the oxide formed is not reliable. Therefore, the method of oxidizing nitride by applying a bias voltage is not feasible to the fabrication of optoelectronic or electronic devices.